This invention pertains to the general field of microbiology, and more specifically to a microorganism culture-transfer device for transferring microorganisms to and from solid media for the purpose of obtaining individual colonies.
Most microbiological laboratories must maintain pure cultures of microorganisms for reference and research. In order to maintain strains of individual microorganisms, the cultures are usually streaked onto plates containing solidified medium. The inoculum of the culture is generally from a single colony on a previously inoculated plate, and the aim of the streaking procedure is to obtain individual colonies of the strain on the fresh plate. Individual colonies of identical form signify to the worker that a single cell type has been transferred; moreover a single colony serves as the inoculum for further strain transfer and experimentation. The transfer technique is generally performed at present with a loop at the end of a long handle. The traditional loop is formed from metal (e.g. platinum or nickel-chromium) which can be quickly heat sterilized (e.g. by flame) and quickly cooled by touching the sterile surface of the fresh medium. Recently, sterile, plastic single-use, disposable loops have been introduced.
In the classic technique, known as streaking, the sterile loop is first brought into contact with the colony whose cells one wishes to transfer; it is then brought into contact with the plate containing sterile solid medium to which one wishes to transfer the cells, and is moved back and forth over the surface of a portion (e.g. one quarter) of the fresh plate. In the initial step, millions of cells may be transferred to the new plate, and must be further diluted by many orders of magnitude so that individual colonies, rather than confluent growth, will be obtained. Since the loop surface is also now contaminated with many thousands of cells, it must be either resterilized (e.g., by flame sterilization in the case of wire loops), or substituted by a new sterile loop (e.g. in the case of single-use, disposable plastic loops). The sterile loop is then brought into contact with the surface of the fresh plate which has been previously streaked, e.g. by several movements across the zone of the first streaking, and then another portion of the plate (e.g. a quarter of the plate adjacent to the first streaking) is streaked. This results in additional dilution of the cells. The loop is then either resterilized or replaced, is brought into contact with the second streaking area, and then a third zone of the plate is streaked. This process must be performed at least three or four times in order to be certain of obtaining individual colonies, rather than confluent growth, following incubation of the fresh plate.